This invention relates to an apparatus for heating limited parts of a human body and more particularly to an ultrasound hyperthermia applicator capable of uniformly heating relatively large volumes locally without scanning.
Hyperthermia is a name which has come to mean high temperature in humans induced with therapeutic intent. Its application to cancer therapy is based on the discovery that malignant cells are generally more sensitive to heat than are normal cells. Physical techniques for hyperthermia include metabolic heat containment, heating by radio frequency or microwave energy absorption, conduction through the skin such as by a hot water bath, and perfusion of externally heated blood, heated intravenous fluids and anesthetic gases, but ultrasound is well known to offer advantages in that it has good penetration in tissue and that ultrasound heating can be focused and localized. The latter characteristic is particularly important because serious damage to healthy tissue and skin in the surrounding region must be avoided. For a given fixed frequency of ultrasound, however, the focal volume size for a single coherent focused transducer cannot be changed so that the treatment of a volume larger than the inherent focal size has previously been done by scanning, but scanning results in a high peak to average power ratio, and also introduces the complex problem of rapidly and accurately scanning the region to be heated.